Thromboembolic disorders, such as stroke, pulmonary embolism, peripheral thrombosis, atherosclerosis, and the like, affect many people. These disorders are a major cause of morbidity and mortality in the United States.
Thromboembolic events are characterized by an occlusion of a blood vessel. The occlusion is caused by a clot which is viscoelastic (jelly like) and is comprised of platelets, fibrinogen and other clotting proteins.
When an artery is occluded by a clot, tissue ischemia (lack of oxygen and nutrients) develops. The ischemia will progress to tissue infarction (cell death) if the occlusion persists. Infarction does not develop or is greatly limited if the flow of blood is reestablished rapidly. Failure to reestablish blood-flow can lead to the loss of limb, angina pectoris, myocardial infarction, stroke or even death. Occlusion of the venous circulation by thrombi leads to blood stasis which can cause numerous problems. The majority of pulmonary embolisms are caused by emboli that originate in the peripheral venous system. Reestablishing blood flow and removal of the thrombus is highly desirable.
There are many existing techniques employed to reestablish blood flow in an occluded vessel. One common surgical technique, an embolectomy, involves incising a blood vessel and introducing a balloon-tipped device (such as the Fogarty catheter) to the location of the occlusion. The balloon is then inflated at a point beyond the clot and used to translate the obstructing material back to the point of incision. The obstructing material is then removed by the surgeon. While such surgical techniques have been useful, exposing a patient to surgery may be traumatic and best avoided when possible. Additionally, the use of a Fogarty catheter is problematic because of the great risk of damaging the interior lining of the vessel as the catheter is being withdrawn.
Percutaneous methods are also utilized for reestablishing blood flow. A common percutaneous technique is referred to as balloon angioplasty where a balloon-tipped catheter is introduced to a blood vessel, typically through an introducing catheter. The balloon-tipped catheter is then advanced to the point of the occlusion and inflated in order to dilate the stenosis. Balloon angioplasty is appropriate for treating vessel stenosis but is not effective for treating acute thromboembolisms.
Another percutaneous technique is to place a microcatheter near the clot and infuse streptokinase, urokinase or other thrombolytic agents to dissolve the clot. Unfortunately, thrombolysis typically takes hours to days to be successful. Additionally, thrombolytic agents can cause severe hemorrhage and in many patients the agents cannot be used at all.
U.S. Pat. Nos. 4,706,671 and 5,011,488 both describe the use of a coiled section for the removal of thromboembolic material. However, neither patent describes a device that is marketed. U.S. Pat. No. 4,706,671 teaches the use of a hollow flexible elastomeric material to form the shape of the coiled section. The coiled section is hollow to allow for the insertion of a liquid into the hollow center such that the coils become stiff. U.S. Pat. No. 5,011,488 teaches the use of a coiled section that is fixed on both the proximal and distal ends such that the operator of the device can change the shape and size of the coils. However, this device may be impossible to manufacture and is impossible to use in small vessels.
Another problematic area is the removal of foreign bodies. Foreign bodies introduced into the circulation can be fragments of catheters, pace-maker electrodes, guide wires, and erroneously placed embolic material such as thrombogenic coils. The only available retrieval devices for the removal of foreign bodies are devices which form a loop that can ensnare the foreign material by decreasing the size of the diameter of the loop around the foreign body. The use of such removal devices is difficult and sometimes unsuccessful.
Thus, there exists a need for the development of a device that can be easily deployed into the circulatory system for the removal of viscoelastic clots and foreign bodies. There is also a need for a device which could be used as a temporary arterial or venous filter to capture and remove thromboemboli formed during endovascular procedures.